Photographic fixer-hardener compositions



Z,87i,l2l Patented Jan. 27, 1959 2,871,121 PHOTOGRAPHIC FDiER-HARDENER COMPOSKTIONS Shuji Kimura, Crystal Lake, and Jules N. Stich, Woodstock, Ill.

No Drawing. Application December 14, 155 Serial No. 552,980 9 Ciaims. (Cl. 96-61) This invention relates principally to improved compositions for the preparation of photographic fixing-hardening baths. More particularly, this invention relates to a dry composition comprising ammonium thiosulfate for the preparation of photographic fixing-hardening baths. Specifically, this invention relates to a dry composition comprising ammonium thiosulfate that remains free flowing even after storage for protracted periods. Even more specifically, this invention relates to a dry composition comprising ammonium thiosulfate that is chemically stable and free flowing even after storage for protracted periods.

As is well known, only a small proportion of the silver halide present in photographic emulsions is utilized in the exposure and development of negatives and prints. After development is complete, it is necessary to remove this excess silver halide in order to produce a permanent negativeor print. The process of removing this excess silver halide is termed fixing and usually involves the treatment of the developed negative or print with a solution containing a material capable of forming a Water soluble complex with silver halides. Sodium thiosulfate pentahydrate (hypo) is the most commonly used fixing agent and is quite suitable for this purpose although it does exhibit several disadvantages, among them being a somewhat deficient fixing power and, more important, a slow fixing rate. Thus, a freshly prepared standard hypo fixing bath requires in the neighborhood of twenty minutes to fix developed film and about ten minutes to fix developed prints. Since the developed but unfixed emulsion contains large amounts of silver halide, it is obviously still sensitive to actinic rays. Accordingly, the fixing process, especially the early stages thereof, must be conducted in the darkroom, and the progress of the process must be checked at frequent intervals since bleaching (loss of some of the previously developed image forming silver particles) results if the negative or print is allowed to remain in the fixing bath for too long a period. It is evident that hypo fixing is a process requiring considerable attention over a considerable period of time for satisfactory'results.

Ammonium thiosulfate (Thiarnate) is an excellent fixing agent and exhibits a considerably greater fixing power and a much greater fixing speed than hypo. Weight for weight, ammonium thiosulfate has three times the fixing power of hypo, that is, the area fixed by a given weight of ammonium thiosulfate is three times as great as the area fixed by an equal weight of hypo. More important, it is easily possible to prepare an ammonium thiosulfate fixing bath that will fix negatives and prints in two or three minutes.

Ammonium thiosulfate, in solid form, cakes readily and is a comparatively unstable compound. During storage in air tight containers ammonium thiosulfate crystals agglomerate into a solid lump and gradually decompose with the production of sulfur which results in a turbid solution when such ammonium thiosulfate is dissolved in water. Accordingly, it has been conventional in the art to market ammonium thiosulfate in the form of a concentrated aqueous solution packaged in glass containers. This has militated against the wide spread adoption of ammonium thiosulfate in the photographic art for obviously, such a marketing system results in inordinately high transportation costs since freight charges are involved in the shipment of the aqueous solvent and the heavy glass carboys to the consumer and in the return of empty carboys to the manufacturer.

Photographic developing, fixing and washing procedures require that the photographic emulsion be immersed in aqueous solutions and in water over extended periods of time. This results in the softening and swelling of the gelatine base of the photographic emulsion, giving rise to a photographic image that is very prone to mechanical injury and disintegration. To overcome this difficulty, it is almost universal practice to use a so-called hardening agent in one of the solutions employed in the processing of negativesand prints, this hardening agent usually being added to the fixing bath. One of the alums is conventionally employed for this purpose. The alums are a well known group of inorganic compounds having the class formula M(SO -N SO -24H O, where M represents a trivalent metal such as aluminum, chromium or iron (ic), and N represents a monovalent metal or a monovalent radical of metallic properties such as sodium, potassium or ammonium. In common usage, the unadorned term alum refers to Al (SO -K SO -24H O and this convention is employed herein.

By controlled heating of an alum, part or all of the 24 molecules of water of crystallization may be removed. Frequently, alums lose a definite number of molecules of water of crystallization at a definite temperature. Thus, ammonium alum, Al (SO (NH SO 24H O, loses 20 molecules of Water of crystallization when heated to C. and becomes completely dehydrated at 200 C. Alum (potassium alum, Al (SO -K SO -24H O) loses 18 molecules of water of crystallization when heated to 64.5" C. and becomes completely dehydrated at higher temperatures. Obviously, the products resulting from the partial or complete removal of water of crystallization from alums are not properly designated alums. In the art it is common practice to refer to the products resulting from the complete or substantially complete removal of water of crystallization from alums as exsiccated alums and this convention will be followed herein.

One object of this invention is to provide a dry composition of matter comprising ammonium thiosulfate that is stable after protracted storage and dissolves in water to produce a fixer-hardener solution.

A further object of this invention is to provide a dry composition of matter comprising ammonium thiosulfate that is free flowing after protracted storage and dissolves in water to produce a fixer-hardener solution.

Another object of this invention is to provide a dry composition of matter comprising ammonium thiosulfate that is stable and free flowing after protracted storage and dissolves in water to produce a fixer-hardener solution.

Additional objects of this invention will become apparent as the description thereof proceeds.

We have found that a dry mixture comprising ammonium thiosulfate and an exsiccated alum remains free flowing and chemically stable during protracted storage and when dissolved in water produces a fixer-hardener solution for photographic purposes.

For the better understanding of our invention, complete descriptions of a number of specific embodiments thereof are presented below but it is to be understood that the particular specific embodiments selected are illustrative only and are in no way to be considered limitations of the scope of the invention.

Example 1 Twenty-five grams ammonium thiosulfate was ground with 6 g. potassium alum, Al (SO -K SO -24H O. The.

resulting mixture was placed in a tightly closed jar. On

contents of the jar were found to be caked.

Example 2 In an experiment run parallel with the one set forth in Example 1, 25 g. ammonium thiosulfate was ground with 4 g. exsiccated potassium alum. The resulting mixture was placed in a tightly closed jar. On the morning following the preparation of the mixture, the contents of the jar were found to be free flowing. On protracted storage the contents of the jar continued to remain free flowing.

Example 3 A composition of matter was prepared by grinding together the following components:

6-. Ammonium thiosulfate 100 Sodium bisulfite (anhydrous) 10 Sodium acetate (anhydrous) 15 Boric oxide 4 Exsiccated potassium alum 15 This composition remained free flowing after protracted storage in a tightly closed container. When dissolved in sufficient water to give 1000 cc. of solution, the resulting solution was clear and was an eminently satisfactory fixerhardener for developed photographic negatives and prints.

Example 4 A composition of matter was prepared by grinding together the following components:

- G. Ammonium thiosulfate 100 Sodium bisulfite (anhydrous) 10 Sodium acetate (anhydrous) 15 Borax (anhydrous) 6 Exsiccated potassium alum 15 The composition remained free flowing after protracted storage in a tightly closed commercial container. Dissolving the composition in sufficient water to give 1000 cc. solution produced a solution that was clear and was an effective fixer-hardener for developed photographic negatives and prints.

Example A composition of matter was prepared by grinding to-' gether the following components:

Ammonium thiosulfate 100 Sodium bisulfite (anhydrous) 10 Sodium acetate (anhydrous) Boric acid 7 Exsiccated potassium alum 15 This composition remained free flowing after protracted storage in a tightly closed commercial container.. Dissolving the composition in sufiicient water to produce 1000 cc. solution resulted in a solution that was clear and an efiective fixer-hardener for developed photographic nega- For example, in producing compositions that re- G. Ammonium thiosulfate 50 to 150 Sodium bisulfite (anhydrous) 5 to 25 Sodium acetate (anhydrous) 15 to 25 Borax (anhydrous) i 4 to .10.. Exsiccated potassium alum 8 to 30 The borax in the above may be replaced, if desired, with 4 to 10 g. boric acid or with 2 to 7 g. boric anhydride. If desired, some sodium thiosulfate (preferably anhydrous) may be incorporated into the compositions of this invention. Thus, the range of mixtures set forth immediately above may contain up to 15 g. anhydrous sodium thiosulfate.

While this invention has been described primarily in connection with the use of exsiccated potassium alum as an essential ingredient of the compositions thereof, this has been done in the interests of simplicity in exposition and it is to be understood that the invention is not limited to the use of this particular exsiccated alum. Other exsiccated alums, for example, exsiccated sodium alum or exsiccated ammonium alum, may be substituted in'lieu of a portion or all of the exsiccated potassium alum employed in the specific formulations set forth above.

As used herein, the term exsiccated alum refers. to a product of the class formula M (SO -N SO produced by the removal of all or practically all of the water of crystallization from an alum, M (SO -N SO -24H,O.

Be it remembered, that while this invention has been described in connection with specific details and specific embodiments thereof, these details and embodiments are illustrative only and are not to be considered limitations on the spirit or scope of said invention except in so far as these may be incorporated in the appended claims.

We claim:

1. The composition of matter comprising a dry powder mixture of ammonium thiosulfate and an exsiccated alum.

2. The composition of matter comprising a dry powder mixture of ammonium thiosulfate and an exsiccated alum, the weight ratio of ammonium thiosulfate to exsiccated alum being in the range 2:1 to 15:1.

3. The composition of matter comprising a dry powder mixture of ammonium thiosulfate and an exsiccated alum, the Weight ratio of ammonium thiosulfate to exsiccated alum being approximately 7:1.

4. The composition of matter comprising a dry powder mixture of ammonium thiosulfate and exsiccated potassium alum.

5. The composition of matter comprising a dry powder mixture of ammonium thiosulfate and exsiccated potassium alum, the weight ratio of ammonium thiosulfate to exsiccated potassium alum being in the range 2:1 to 15: l.

6. The composition of matter comprising a dry powder mixture of ammonium thiosulfate and exsiccated potassium alum, the weight ratio of ammonium thiosulfate to exsiccated potassium alum being approximately 7:1.

7. The composition of matter comprising a dry powder mixture of ammonium thiosulfate and exsiccated sodium alum.

8. The composition of matter comprising a dry powder mixture of ammonium thiosulfate and exsiccated sodium alum, the weight ratio of ammonium thiosulfate to exsic cated sodium alum being in the range 2:1 to 15 :1.

9. The composition of matter comprising a dry powder mixture of ammonium thiosulfate and exsiccated sodium alum, the weight ratio of ammonium thiosulfate to exsiccated sodium alum being approximately 7:1.

References Cited in the file of this patent 1 UNITED STATES PATENTS OTHER REFERENCES Journal Soc. of Chem. Ind., Trans. Abstracts, volume 39(1920) (pages -108). 

1. THE COMPOSITION OF MATTER COMPRISING A DRY POWDER MIXTURE OF AMMONIUM THIOSULFATE AND AN EXSICCATED ALUM. 